110 



LOWER INVERTEBRATES. 



animal, but in Ocyroe these lateral developments take on the form of wings or similar 

 bodies. Cestus moves through the water by a slight undulation of the body, while 

 Ocyroe does the same by a flapping movement of its greatly developed lateral lobes, 

 and by their beating upon the surrounding water. "When Ocyroe is at rest, the lateral 

 wings are widely extended, giving to the animal a remote likeness to Cestus. "When, 

 however, motion is attempted, the lobes are raised above the horizontally extended 

 position which they occupy at rest, and then violently swung downward, passing 

 through almost 180°. This flapping of the two wings in concert is continued several 

 times, and in that way the animal is propelled through the water. The function of 

 the rows of combs in the movements of the medusa is secondary to the flapping move- 

 ments of the lateral wings. 



The body of Ocyroe, from two sides of which the wings arise, is of oblong, oval 

 shape, with a mouth at one pole, and a cluster of otoliths in an otocyst at the opposite. 

 There is no vestige of tentacular appendages near the mouth, and the lips are undi- 



Fjg. 104. — Ocyroe crystaltlna. 



vided, smooth, and highly flexible. Ocyroe thus far has been taken only from the 

 waters of tropical America. 



In colder latitudes as on our Xew England coast, we have a beautiful ctenophore 

 called Bolina, and another very closely allied genus known as Mnemiopsis. These 

 medus£e are in many respects most closely allied to Ocyroe, or rather Ocyroe seems an 

 aberrant form of these more northern jellj-fishes. Although the same lateral lobes 

 exist in both genera, their importance in JBolina, as far as movement is concerned, is 

 much less than in Ocyroe. They are also seldom or never carried extended horizon- 

 tally at right angles to the body, as in the curious genus Ocyroe. Holina is one of the 

 most transparent of the comb-bearing medusae. The body is very gelatinous and 

 highly phosphorescent. The sides of the body are developed into two larger lappets or 

 lobes which are carried or hang vertically instead of horizontally. On account of the 

 contractile powers of the body walls, Bolina can vary its outlines very considerably ; as 

 a rule, however, when the body is seen from the side, it has an oval or elongated foi-m. 

 Eight rows of vibratile combs contribute to the propulsion of the medusa through the 

 water. These lie upon the external surface of the body, and arising from the pole 

 opposite the mouth-opening, extend to the more distal edge of the lateral expansions 

 to the vicinity of the mouth. From the great development of the lateral lobes, the 

 four lines of vibratile combs which cross these bodies are much longer than those 

 'which lie on the body regions between them. Two tentacles are found hanging from 

 the sides of the body of Bolina. These tentacles are of diminutive size in the adult, 

 and are remnants of structures which in early conditions of growth were very much 

 more developed. 



